Food processing method for edible and perishable plants

ABSTRACT

The present invention makes it possible to kill both the cells and the microorganisms of edible and perishable plants and at the same time to cause the cellular resolution by autolytic enzymes, and to change undesirable characteristics for foods such as harshness, bitterness, astringency, grassiness and the like into desirable characteristics such as tastiness, sweetness, and flavors.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a food processing method for edible andperishable plants such as vegetables and fruits.

BACKGROUND ART

Foods such as vegetables and fruits are largely divided into non-heatedfoods (raw foods) and heated foods. Very few in between these two statesare produced. Non-heated foods are further divided into ones whose cellsare alive (edible) and perishable plants such as salad and fresh fruit)and the others whose cells are dead (pickles, that is tsukemono, andvinegar pickles). Some foods have toxicity, bitterness, astringency,harshness, grassiness and the like to protect themselves againstanimals, insects and the like, under the condition that their cells arealive. On the other hand, when their cells die, edible plants areswiftly resolved by autolytic enzymes and so become easy to eat anddigest.

Numerous microorganisms are attached to a surface of edible andperishable plants. Usually, even after being washed, the plants retainmicroorganisms in which the number of bacteria is between 10⁴ and 10⁶per gram. As there have frequently occurred food-poisoning in recentyears, the foods are commonly washed in a germicidal agent such assodium hypochlorite solution. But a complete sterilization is difficult,and rinsing the foods after the above treatment to remove the germicidalagent largely decreases their quality. As a result, many schools havegiven up providing their pupils with raw vegetables (salad) for lunch.

On the other hand, in the case of pickles and vinegar pickles of anon-heated type and whose cells are dead, a method is adopted in whichmicroorganisms are controlled from reproducing while their cells arebeing killed by an osmotic pressure of salt, sterilizing power ofvinegar and the like. In this case, however, the low temperature and thesalt restrain the resolution of the cells by autolytic enzymes, so thatit takes a long processing time, which makes the pickles and the vinegarpickles much too salty and sour. Pickles using highly concentrated saltto preserve them from rotting should be exposed to water so as to removethe salt. Accordingly the tastiness factor and nutritive elements aregreatly damaged, and the real situation is that the use of additiveshelps the pickles stay tasty for longer days. Furthermore, as asubstantial amount of water is used (usually 50 tons of water is used tomake one ton of pickles), waste water disposal becomes very costly.

In the case of heating edible plants, their tissue softens, and thefactors such as harshness, grassiness and the like disappear. But therapid heating makes the cellular resolution by autolytic enzymesinsufficient, the foods lose their original taste, and nutritiveelements (especially Vitamin C) are greatly damaged.

The technologies of processing edible and perishable plants by heatingat a medium temperature include a method of processing vegetables in awarm aqueous solution of a medium temperature range (between 40° C. and70° C.) (Japanese Patent Laid-open Publication No. 5-68505), one ofmaking pickles by steaming them (Japanese Patent Laid-open PublicationNo. 6-169690), one of sterilizing and preparing foods by steaming them(Japanese Patent Laid-open Publication No. 11-155513), one of picklingJapanese apricots with salt while maintaining a high atmospherictemperature (Japanese Patent Laid-open Publication No. 9-65824), one ofmaking pickles in a highly concentrated saline solution of a mediumtemperature (Japanese Patent Laid-open Publication No. 8-289722), one ofwashing vegetables in a warm aqueous solution of between 35° C. and 55°C. (Japanese Patent Laid-open Publication No. 11-18740), and so on.These methods, however, do not fix the temperature range from theviewpoint of cellular resolution by autolytic enzymes, so that the foodshave neither tastiness nor sweetness.

Since edible and perishable plants are alive, nutritive substances ofthe tissue are lost by metabolism as time passes, so that the plantswither, become fibrous and less tasty. In due time, they develop moldfrom the parts where the cells died from such as cuts, and rot all over.Perishable vegetables keep only for a week or so at the longest.Perishable fruits keep longer than vegetables but about one month is thelimit.

Generally, perishable plant foods have hard cell walls, lack flexibilityand contain a lot of water (80-95% of them is water) as compared withanimal foods. Therefore, their cells are greatly destroyed by freezingand a large amount of exudate, i.e. “drip”, flows out when defrosting.In addition, browning, softening and rotting are caused by enzymes.Accordingly, it is said that perishable plant foods are not suitable forfreezing.

On the other hand, frozen processed vegetables and fruits arecommercially available. In this case, vegetables and fruits are cut intosmall pieces and blanched, that is to say, dipped into hot salt water ofa high temperature for a short time (for example, 90° C.×10 seconds-1minute) by way of treatment before freezing. This heating treatmentsoftens the tissue, deactivates the enzymes and fixes chlorophyll, whichprevents the products from becoming low in quality while they are keptfrozen as well as when they are defrosted.

Since blanching means cooking by heating, it is inevitable that bothtexture and nutritive substances of perishable foods are lost.Furthermore, the shortness of heating time makes the equal-treatmentdifficult, resulting in variation in quality. On top of it, withoutcellular resolution by autolytic enzymes, harshness and grassinessremain, and the original taste of the foods is lost.

Since non-heated processed foods, for example, pickles, whose cells aredead, have been dehydrated with salt, and the cell walls have beendestroyed, the foods are hardly damaged by freezing. It has already comeinto practice to store heavily salted pickles such as nozawana andtakana, whose tissues are comparatively solid, in a freezer.

The cells of edible and perishable plants are alive. If the plants areleft as they are, they show signs of nutritive deterioration and changein taste, which decreases their commercial value. Considering the above,edible and perishable plants should be cooked as soon as possible orstored in a freezer. When the cells die, the plants begin to be resolvedby autolytic enzymes, but at the same time they are attacked by themicroorganisms attached to them and rotting progresses.

An object of the present invention is to offer a food processing methodfor edible and perishable plants, which kills both the cells and themicroorganisms of them, as well as causes the cellular resolution byautolytic enzymes, and accordingly changes undesirable components forfoods (harshness, bitterness, astringency, grassiness and the like) intotastiness, sweetness, sourness and flavors.

A further object of the present invention is to offer a food processingmethod for edible and perishable plants which is excellent for storingthem in a freezer, in addition to the above advantages.

SUMMARY OF THE INVENTION

In order to accomplish the above and other objects, the presentinvention provides the following food processing method for edible andperishable plants. An aqueous solution with a higher osmotic pressurethan that of targeted edible and perishable plants is prepared andheated, retaining a certain range of temperatures which practicallykills cellular tissues of the above edible plants and microorganismsattached thereto, but does not substantially discourage the autolyticenzymes both inside and outside the cells of the above edible plants,this heated aqueous solution is brought into contact with the abovetargeted edible plants, thereby killing most of the cells of the aboveedible plants, causing cellular resolution by autolytic enzymes, andalso conducting low-temperature sterilization treatment, thereafter theabove edible plants are processed into foods.

Moreover, in a food processing method for edible and perishable plantsof the present invention, the above heated aqueous solution is broughtinto contact with the targeted edible plants, thereby killing most ofthe cells of the above edible plants, causing cellular resolution byautolytic enzymes and also conducting low-temperature sterilizationtreatment, thereafter the above edible plants are brought into contactwith a cooling solution and are processed into foods after having beencooled and stored in a freezer.

It is preferable that the above heated aqueous solution has an osmoticpressure of 10 atm or higher, and a temperature higher than 55° C. butlower than 60° C.

As the osmotic pressure of almost all edible and perishable plants islower than 10 atm, the osmotic pressure of the aqueous solution must be10 atm or higher. If the latter osmotic pressure is lower than 10 atm,the targeted plants absorb water, which destroys the flavor, and becomedifficult to handle after the treatment. In order to attain this osmoticpressure, the aqueous solutions of foods or food additives with a highosmotic pressure are preferable. For example, inorganic salts such assalt and calcium chloride, edible saccharides such as sucrose andglucose, organic acids or related salts such as acidulants, fermentedvinegar and fruit vinegar, and alcoholic drinks may be used.

Here are examples of the substances with an osmotic pressure of 10 atmas compared with the concentration of aqueous solutions: salt 1.2% ofweight, sucrose (disaccharide) 12% of weight, glucose (monosaccharide)6% of weight and ethyl alcohol 1.3% of weight. These substances may beused alone or as a mixture of two or more thereof. The osmotic pressurecan be easily calculated because in general it is inversely proportionalto the molecular weight of a substance and proportional to itsconcentration.

It is desirable that edible and perishable plants are in contact with anaqueous solution having an osmotic pressure of 10 atm or higher and atemperature between 55° C. and 60° C., so that most of the cells, thatis 50% or more, or preferably 60% or more, are killed. In this range oftemperatures, low and medium temperature bacteria which are the majorsource of food poisoning and putrefaction will be mostly (95% or more)killed. Although the control time depends upon the shapes, sizes andphysical properties of the plants, it is generally in the range of 1 to30 minutes.

The most effective way to resolve the compounds inside and outside thecells and make them homogeneous is to utilize the autolytic enzymeeffect which causes the destruction of the cell walls and cuts up bigmolecules such as polyphenol, cellulose, polysaccharides, proteins andthe like.

For this purpose, it is indispensable to keep a temperature of 60° C. orlower at which the enzymes are not deactivated. That is to say, byundergoing a process in which the temperature is kept between 55 to 60°C. at which the cells die but the enzymes are not deactivated, theprocessability and preservative quality thereafter will be greatlyimproved.

The above-mentioned treatment with a warm aqueous solution at atemperature of 55 to 60° C. is suitable for foods, because in thistreatment, nutritive elements such as vitamin C, which are easilydestroyed by heat, are not damaged, chlorophyll is fixed, the color willfade more slowly, and microorganisms largely decrease in number.

In addition, preferably the above cooling solution has an osmoticpressure of 5 atm or higher, and a temperature of 15° C. or lower.

It is advisable that a process in which the above edible and perishableplants are brought into contact with the above heated aqueous solutionand/or with the above cooling solution, is conducted by soaking theabove edible and perishable plants in the above heated aqueous solutionand/or in the above cooling solution, or by spraying the above heatedaqueous solution and/or the above cooling solution on the above edibleand perishable plants.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart showing a food treatment process of edible andperishable plants of the present invention;

FIG. 2 is a diagram briefly showing a batch-type treatment equipment tobe used when implementing a method of the present invention; and

FIG. 3 is a diagram briefly showing a sequence-type treatment equipmentto be used when implementing the method of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[A] The implementation of the present invention will now be described indetail based on FIG. 1 showing the treatment process of edible andperishable plants.

(1) Targeted Vegetables and Fruits

The targets are perishable vegetables, such as green vegetables(spinach, mustard spinach, Chinese cabbage, cabbage, and the like),stalk vegetables (asparagus, broccoli, cauliflower, onion, and thelike), fruit vegetables (cucumber, tomato, melon, strawberry, and thelike), root vegetables (turnip, carrot, Japanese radish, scallion(rakkyo), ginger, sweet potato, potato, taro, yam, and the like) andvarious mushrooms (hen-of-the woods fungus, oyster mushroom, shimeji,shiitake, mushroom, and the like) as well as perishable fruits (Japaneseapricot, apricot, apple, cherry, peach, pear, and the like).

(2) Washing

Agricultural products must be washed because microorganisms and foreignsubstances in the soil are attached to them. In order to wash and removevarious foreign substances such as soil, sand, dead leaves, roots,insects and their larvae, slugs, snails, frogs, hair and the like, it isefficient for the targets to be soaked in a rinse tank, or to be sprayedwith wash water. Using surface active agents or germicides together withthe above washing is also effective.

(3) Cutting into Suitable-Sized Pieces

As the targeted plants have different shapes, sizes and physicalproperties, it is necessary to adjust their shapes and sizes in order toheat them equally and evenly. Cubic, cylindrical or globular shapes of50 mm or under in thickness or in diameter are desirable. For example, aJapanese radish is cut lengthwise in half or in four, or cut in roundslices of 50 mm or less in thickness. Cucumbers, Japanese apricots,strawberries and the like are used whole. Green vegetables, stalkvegetables or various mushrooms can be used whole, or cut in half orfour.

(4) Treatment in a Warm Aqueous Solution

The targets are brought into contact with a 55° C. to 60° C. aqueoussolution to kill the cells and cause the resolution of them by autolyticenzymes. At this time, the osmotic pressure of the aqueous solution mustbe 10 atm or higher (in the case of salt, 1.2% of weight or more), so asto prevent the targets from absorbing water.

The contact time must be decided based on the heat transfer velocity(specific surface area, density, thermal conductivity) and the sizes(thickness in particular) of the targets. The suitable time examplesrequired for each vegetable are as follows:

25-30 minutes for Japanese radish (cut lengthwise in four), 15-20minutes for cucumbers (whole), 8-12 minutes for scallions/asparagus(whole)/Chinese cabbage (cut into pieces), 5-7 minutes for variousmushrooms, 2-5 minutes for spinach/mustard spinach, 10-15 minutes forJapanese apricots/strawberries.

Ideally, the weight of an aqueous solution required for heating is 2 to30 times, preferably 3 to 20 times that of the targets. Using the samesolution several times makes the treatment more efficient.

The products become more flexible after they are treated, so that theshapes may be changed. Green vegetables become easy to handle thereafterbecause the volume decreases considerably. This treatment loses nonutritive substances, and moreover, drastically decreases (to onehundredth or so) the number of microorganisms.

(5) Solution Removal

The solution attached to the products is removed by fall due to gravity,by use of centrifugal separators, by blowing clean air thereon, or bywiping with such as paper or cloth.

(6) Cooling

The heated targets must be cooled except those to be processedimmediately, in order to maintain their quality. The concentration of acooling solution may be lower than that of a warm aqueous solutionbecause the surfaces of the targets have been already heated, theircells are dead and an aqueous solution with a high osmotic pressure haspenetrated into them. For practical use, a cooling solution with anosmotic pressure of 5 atm or higher (in the case of salt 0.6% by weightor more) and a temperature retained at 15° C. or lower is desirable.

(7) Freezing

IQF (Individual Quick Freezing) method using various freezers such astunnel freezers of air blast type or liquid nitrogen type, contactfreezers makes it easy to handle the products after they are frozen.

(8) Storage in a Freezer

The products must be kept in a −20° C. class freezer. Glazing orairtight packing is effective for preventing the products from becomingdry while they are kept in a freezer.

(9) Defrosting

Although the products can be defrosted while they are left as they are,it is more efficient to use a warm saline solution defrosting machine(Japanese Patent Laid-open Publication No. 9-215468).

(10) Preparation and Processing

By using normal cooking methods, ingredients of salads, foods preservedin salt (lightly pickled vegetables, pickles, seasoned pickles, and thelike), seasoned dishes (soused greens, cooked salads, and the like),fermented foods/pickled foods in vinegar (kimchi, sauer kraut, pickles,marinade, and the like), foods processed with sugar (jam, fruit wine,candied fruit, and the like) and heated foods (simmered food, steamedfood, grilled food, deep fried food, lightly-fried food, and the like),as well as frozen foods which are intermediate ingredients, are preparedand processed.

(11) Packaging

The products are packed airtight in a container or a bag, both made ofeither paper or plastic. If necessary, deaeration packaging, gaspackaging and the like can be used.

(12) Distribution at Low Temperature

As the aim of the present invention is to provide food products using nogermicides and also limiting preservatives and food additives as much aspossible, product distribution under cold or frozen conditions isessential.

[B] Equipment examples of the present invention are explained in FIGS. 2and 3.

Batch-Type Treatment Equipment (FIG. 2)

A targeted edible and perishable plant “A” having been cut intosuitable-sized pieces (50 mm or less in thickness) and washed, isprocessed by a batch-type treatment equipment “1”.

A basket “2” is made of a net and/or a perforated plate material, intoand out of which an aqueous solution goes freely but the target “A” isunable to flow out. To prevent the target “A” from surfacing, the basketis equipped with a removable lid “3” on its top.

The ceiling is equipped with a traversing rail “4” with a hoist, whichenables the basket “2” to run up and down, and also from side to side.This can be done either manually or mechanically.

A heating tank “11” is a tank that holds a heated aqueous solution andis large enough to include the entire basket “2”.

A circulation pump “12” is used to circulate an aqueous solution in theheating tank. The solution is passed through a filter “13” to removeforeign matters, is moved into a heater “14” to control its temperatureto a required range of degrees, then is put back into the heating tank“11” so that the solution may be kept at an even temperature in it.

The target “A” which has been heated for a required time is liftedtogether with the basket “2”, and the solution having been drained, istransferred to a cooling tank “21”. The cooling tank “21” is preferablysimilar to the heating tank “11”, and a cooling solution is circulatedin a circulation pump “22”.

The cooling solution is filtered by a filter “23”, moved into a cooler“24” to control its temperature, and put back into the cooling tank 21so that the solution may be kept at an even temperature in it.

The target “A” which has been cooled for a required time is lifted, istaken out from the basket after the solution is drained, then moves onto a subsequent process.

The above-mentioned treatment may be automatically conducted by sequencecontrol, which helps save labor. In addition to that, it is possible toeven the temperature as well as to shorten the required treatment timeby shaking the target “A” mechanically or by applying a supersonic waveto the solution and shaking it.

Sequence-Type Treatment Equipment (FIG. 3)

A targeted edible and perishable plant “A” having been cut into suitablesized pieces (50 mm or less in thickness) and washed, is put into asequence-type treatment equipment “30” and then is placed on a mainconveyor “32” via a conveyor “31”.

The main conveyor “32” is connected to a discharge conveyor “37” througha heating part “33”, a solution-draining part “34”, a cooling part “35”and the other solution-draining part “36”. The target “A”, going throughthe above line, is carried from the discharge conveyor “37” to asubsequent process.

The main conveyor “32” is an endless type one with driving parts at bothends, and is made of porous material (net, perforated plate material orthe like) and moves the target “A” continuously.

A heating tank “41” is designed in such a way that the solution stays atits bottom. The solution is carried by a circulation pump “42”, passedthrough filter “43” to remove foreign matters, moved to a heater “44” tocontrol its temperature to a required range of degrees, and then sprayedby both upper and lower sprays “45” and “46” to heat the target “A”. Thevolume of the circulated solution is desirably between 10 and 20 timesthat of the target to be treated.

The heated target “A” is carried to the cooling part “35” via thesolution-draining part “34”.

A cooling tank “51” is designed in such a way that the solution stays atits bottom. The solution is carried by a circulation pump “52”, passedthrough a filter “53” to remove foreign matters, moved to a cooler “54”to control its temperature, and then sprayed by both upper and lowersprays “55” and “56” to cool the target “A”.

It is also effective that the solution draining parts “34” and “36” areequipped with solution-draining measures such as spraying clean air onthe target so that the solution should not be brought out from bothparts (not described in this figure).

The time required for the target to be contacted with the solution canbe selected freely depending on the velocity of the main conveyor “32”.The cooling time required should be between 50 and 100% to the warmingtime. The length ratio of the heating part “33” and the cooling part“35” of the conveyor is preferably the same as the above ratio of thetime.

In this sequence-type treatment equipment “30”, it is possible tomobilize the target “A” by controlling pressure, solution flow quantity,and angles of upper and lower sprays “45”, “46”, “55” and “56”, so thatproducts of even quality can be produced quickly. Furthermore it is easyto make the system completely airtight and it is also rather easy to addan automatic washing function, both of which are effective at preventingthe target from being polluted with microorganisms.

The above-mentioned equipment shows only one example to implement themethod of the present invention, and the equipment applicable to thepresent invention is not to be limited to the above example.

EXAMPLE 1

As Sample 1A, 5 whole cucumbers (approximately 500 g) were immersed in 4liters of a 14% by weight saline solution kept between 56-59° C., leftto soak for 20 minutes, then transferred and soaked in a 2% by weightcold saline solution (0-5° C., 4 liters) for 20 minutes to cool them.The same kind and number of non-treated whole cucumbers in the same lotwas used as Sample 1B. The number of living bacteria, quantity ofvitamin C, and salt content for samples 1A and 1B were analyzed at JapanFood Research Laboratories. The results are as follows:

TABLE 1 The analysis of the cucumbers Methods of analysis (Sample 1A)The number of 300 or less/g Standard agar plating method living bacteriaVitamin C 9 mg/100 g High performance liquid chromatography Salt 836mg/100 g Atomic absorption spectrometry (Sample 1B) The number of 5.7 ×10⁴/g Standard agar plating method living bacteria Vitamin C 9 mg/100 gHigh performance liquid chromatography Salt 5 mg/100 g Atomic absorptionspectrometry(Evaluation)

There occurred neither change of weight nor loss of nutritive substancesby treatment in a warm aqueous solution, the number of living bacteriagreatly decreased, and the salt content was low. Sample 1A was edibleraw and tasted like lightly salted pickles or salad.

EXAMPLE 2

The cucumbers in samples 1A and 1B of Example 1 were cut into piecesabout 5 cm long, pickled in the following way, and compared.

TABLE 2 Ingredients for making cucumber pickles cucumbers (pieces 5 cmlong) 500 g 10% acid vinegar 200 cc water 500 g sugar 200 g glucose 200g(Evaluation)

After having been kept in a refrigerator for 2 weeks, Sample 1A (thepresent invention) was still deep green and tasted good, but Sample 1B(non-treated) browned, went bad and was not good to eat.

EXAMPLE 3

As Sample 2A, 700 g of a half Chinese cabbage (lengthwise cut) was cutinto pieces 5 cm wide, placed in a net bag and soaked in 4 liters of a14% by weight saline solution kept between 56-59° C. for 12 minutes,then transferred and soaked in a 2% by weight cold saline solution (0-5°C., 4 liters) for 12 minutes to cool them. The other half Chinesecabbage (non-treated) was used as Sample 2B for comparison. The numberof living bacteria, quantity of vitamin C and salt content for samples2A and 2B were analyzed by Japan Food Research Laboratories.

The results are as follows:

TABLE 3 The analysis of the Chinese cabbage (cut) Methods of analysis(Sample 2A) The number of 5.6 × 10³/g Standard agar plating methodliving bacteria Vitamin C 13 mg/100 g High performance liquidchromatography Salt 1150 mg/100 g Atomic absorption spectrometry (Sample2B) The number of 2.1 × 10⁵/g Standard agar plating method livingbacteria Vitamin C 13 mg/100 g High performance liquid chromatographySalt 12 mg/100 g Atomic absorption spectrometry(Evaluation)

There occurred neither change of weight nor loss of nutritive substancesby treatment in a warm aqueous solution, the number of aerobic bacteriagreatly decreased, and the salt content was low. Sample 2A was edibleraw and tasted like lightly salted pickles or salad.

EXAMPLE 4

The two halves of Chinese cabbage, 500 g each in samples 2A and 2B weredressed with kimchi seasoning shown in Table 4, and kept in arefrigerator for 3 days.

TABLE 4 kimchi seasoning ground chili pepper  5 g salt-cured preserve ofsquid 10 g garlic  1 piece ginger  5 g sugar 10 g(Evaluation)

After having been kept in a refrigerator for 3 days, Sample 2A (thepresent invention) was well pickled, with a Kimchi flavor and tastedgood, but Sample 2B (non-treated) was raw Chinese cabbage with no kimchiflavor.

EXAMPLE 5

300 g of fully ripened Nanko-ume (the most representative and highquality Japanese apricot) was placed in a net bag and soaked in 4 litersof a 15% by weight saline solution kept between 55.5-58.5° C. for 15minutes to treat them in a warm aqueous solution. These treated Japaneseapricots, after having been slightly drained, were placed in a one-literglass bottle, 150 g of sugar and 500 cc of white liqueur (alcohol 35%,cooled to 2° C.) were added, and the bottle was left as it was at roomtemperature for 4 weeks and stirred occasionally.

The Japanese apricots completely sank to the bottom in 4 weeks, andlight-colored transparent Umeshu (ume brandy) was obtained.

The evaluation was that there was no great difference in flavor betweenthis and the one obtained from non-treated Japanese apricots which wereprocessed and soaked for 8 months in the same way as the above. (Anevaluation made by all 5 panelists.)

EXAMPLE 6

As Sample 3A, 500 g of shaped scallions were placed in a net bag and wassoaked in 4 liters of a 12% by weight sugar and 3% by weight salinesolution kept between 55.5-58.5° C. for 8 minutes, then soaked in 4liters of a 1% by weight cold saline solution kept between 5-10° C. for6 minutes to cool it.

On the other hand, as Sample 3B, the same kind and volume of scallionsin one lot was dipped in a 3% by weight hot saline solution (90° C.) for30 seconds for blanching, then dipped in a cold aqueous solution keptbetween 0-2° C. for 2 minutes.

Each of samples 3A and 3B, after the solution was wiped off, was placedside by side on an aluminum tray, frozen in a direct-freezing typefreezer (Toshiba Corporation, GR-274SV) for one hour, then moved into aplastic vessel, and kept in a −20° C. freezer for one month.

Liquid seasoning shown in Table 5 was poured on samples 3A and 3B whichwere kept in a frozen condition, then the samples were kept in arefrigerator for one month.

The evaluation was that the scallions of the present invention werewhite, lustrous, and crisp with a sharp taste and strong flavor, ascompared with the blanched ones. (An evaluation made by all 5panelists.)

TABLE 5 Composition of liquid seasoning corn vinegar (4.2%) 400 cc water320 cc sugar 200 g salt  40 g

EXAMPLE 7

A bundle of spinach (200 g) was soaked in 4 liters of a 3% by weightsaline solution kept between 55.5-58.5° C. for 2 minutes, then soaked ina 1% by weight cold saline solution (10-15° C., 4 liters) for oneminute, lightly squeezed to drain, and was cut to a length of 4 cm. Thepieces were then placed vertically on an aluminum tray, frozen in adirect-type freezer for 2 hours, put into a bag of barrier plastic, andkept in a −20° C. freezer for 3 months.

The evaluation after defrosting was as follows:

-   {circle around (1)} bright green color, {circle around (2)} little    dripping, {circle around (3)} the tissue being solid and chewy,    {circle around (4)} texture close to raw compared with commercially    available, blanched frozen products.

EXAMPLE 8

300 g of maitake mushroom (whole) was soaked in 4 liters of a 1.5% byweight saline solution kept between 55.5-58.5° C. for 3 minutes, thenimmediately transferred and soaked in a 1% by weight cold salinesolution (10-15° C., 4 liters) for 2 minutes to cool it, left as it wasfor 3 minutes to drain solution. Then it was placed on an aluminum tray,frozen in a direct-type freezer-refrigerator for 2 hours, put into a bagor barrier plastic, and kept in a −20° C. freezer for one month. Forcomparison, non-treated maitake mushroom was frozen and kept in afreezer in the same way.

The evaluation after defrosting shows that the products of the presentinvention had the following characteristics compared with thenon-treated ones.

-   {circle around (1)} little dripping, {circle around (2)} deep brown    color, {circle around (3)} little harshness, {circle around (4)} the    tissue is solid.

EXAMPLE 9

300 g of Nyohou brand strawberries of medium size were soaked in 4liters of a 6% by weight fructose solution kept between 55.5-58.5° C.for 12 minutes, then cooled in a 3% by weight fructose solution (10-15°C., 2 liters) for 8 minutes, left as is on a wire gauze for 3 minutes todrain the solution. After the solution was drained, the strawberrieswere placed on an aluminum tray, frozen in a direct-typefreezer-refrigerator for 1 hour, then put into a plastic vessel, andkept in a −20° C. freezer for 2 months.

The strawberries, after defrosting, retained their shape and bright redcolor, and were fully edible raw. (An evaluation made by all 5panelists.)

EXAMPLE 10

600 g of Housui brand pears were peeled, cored out and cut into 1.5-2.0cm cubes, then soaked in 4 liters of a 6% by weight saline and 1.2% byweight citric acid solution kept between 55.5-58.5° C. for 12 minutes.After that, the pears were left as they were on a wire gauze for 3minutes to drain solution, put into an earthen pot adding 360 g ofrefined white sugar, and cooked for 30 minutes over low heat whileremoving the scum to make jam.

The evaluation reveals that the products of the present invention hadthe following characteristics as compared with the non-treated ones.

-   {circle around (1)} shorter cooking time (60 minutes required for    the non-treated ones), {circle around (2)} the flavor of pears    greatly retained, {circle around (3)} light color and nearly    transparent, {circle around (4)} sour with well-balanced sweetness.    (An evaluation made by all 5 panelists.)

EXAMPLE 11

300 g of carrots (peeled, cut into 3-4 cm cubes) were soaked in 4 litersof a 3% by weight saline solution kept between 55.5-58.5° C. for 20minutes. After that the cubes were left as they were on a wire gauze for5 minutes and drained, then boiled in water for 12 minutes. Forcomparison, non-treated carrots were boiled in water under the sameconditions.

The evaluation of the products of the present invention shows that thefollowing characteristics as compared to those of the non-treatedcarrots were seen.

-   {circle around (1)} deep in color, {circle around (2)} moderately    chewy, {circle around (3)} not much falling apart while boiling,    {circle around (4)} the peculiar flavor and taste of carrots being    strong. (An evaluation made by all 5 panelists)

EXAMPLE 12

500 g of 3 Beniazuma brand sweet potatoes (the most popular sweet potatoin Japan, 30-35 mm in diameter×20 cm long) were soaked in 4 liters of a3% by weight saline solution kept between 56-59° C. for 20 minutes.After that the sweet potatoes were left as they were at room temperaturefor one hour to return to an ambient temperature (Sample 4). The sweetpotatoes (Sample 4) were heated in a 500-watt microwave oven for 10minutes to make fukashiimo (steamed sweet potatoes). For comparison,non-treated sweet potatoes were heated in a microwave oven in the sameway.

Compared with the non-treated ones, the products of the presentinvention had the following characteristics:

-   {circle around (1)} Dry inside and not soggy at all, {circle around    (2)} very sweet, {circle around (3)} strong flavor that sweet    potatoes inherently retain.

Regarding the storage of Sample 4 (the present invention), the followingfinding was obtained:

-   {circle around (1)} No low-temperature damage when stored at 5° C.,    {circle around (2)} No quality deterioration when kept at −20° C. in    a freezer.

EXAMPLE 13

34 liters of a 7% by weight saline solution was put into a warm salinesolution tank of the New-Texture Vegetable Processing Equipment (#100,manufactured by Terada Seisakusho Co., Ltd., Shizuoka Prefecture) andthe temperature was kept between 55.5-58.5° C. While, 33 liters of a0.7% by weight saline solution was put into a cold saline solution tankof the above equipment and the temperature was kept between 9-11° C.

3 kg of onions sliced lengthwise at 1-2 mm wide were placed in a basket,soaked in a warm saline solution tank for 2 minutes, transferred andsoaked in a cold saline solution tank for 2 minutes, then left as itwere to drain for 3 minutes, and finally evaluated.

The characteristics of the products of the present invention were asfollows:

-   {circle around (1)} The number of living bacteria* 4.4×10³/g    -   Coliform group** negative

In the case of the non-treated sliced onions, however, the results were:

-   -   The number of living bacteria* 1.2×10⁵/g    -   Coliform group** 16/g        -   *Petrifilm™—AC culture medium        -   **Petrifilm™—CC culture medium

-   {circle around (2)} Moist, sharp taste remained and also very sweet.

-   {circle around (3)} most suitable for marinade material

1. A food processing method for edible and perishable plants comprisingthe steps of: preparing an aqueous solution with a higher osmoticpressure than that of said plants to be processed; heating said aqueoussolution to a temperature in the range of 55° C. to 60° C., which ishigh enough to kill cells of said plants and microorganisms attachedthereto; bringing said solution into contact with said plants whilekeeping said temperature range for a time period required to killsubstantial amount of said cells and substantially all of saidmicroorganisms and cause enzymatic resolution by autolytic enzymes ofsaid plants; and bringing said plants into contact with a coolingsolution in succession to said contact with said aqueous solution for atime period which is equal to 50-100% of said heating time, said coolingsolution having an osmotic pressure of 5 atm or higher and a temperatureof 15° C. or lower.
 2. A food processing method for plants as set forthin claim 1, wherein said aqueous solution has an osmotic pressure of 10atm or higher.
 3. A food processing method for plants as set forth inclaim 1 or 2, wherein said plants are brought into contact with saidaqueous solution and/or said cooling solution by soaking said plants insaid aqueous solution and/or said cooling solution.
 4. A food processingmethod for plants as set forth in any one of claim 1 or 2, wherein saidplants are brought into contact with said aqueous solution and/or saidcooling solution by spraying said aqueous solution and/or said coolingsolution on said plants.